Although it is now well accepted that the primary anticaries activity of fluoride (F) is via topical action, the importance of F retention in the mouth has not been elucidated. The intent of this proposal is to study the relationship between F retention in the oral cavity and the clinical efficacy of home-use topical F products. In the first phase of the project F concentrations in whole saliva, ductal saliva, plaque, enamel, soft tissue and interproximal spaces will be determined at different intervals after the application of topical F products (F-dentifrice, F- mouthrinse, F-gel). Four subject panels will be compared: a standardized panel of dentally healthy adults; an edentulous panel; a periodontally involved panel; and an hyposalivatory panel. In the second phase of the project the standardized subject panel will wear an intraoral appliance carrying partially demineralized blocks of human enamel. Enamel remineralization and F-uptake will be evaluated after 1, 7 and 14 days of treatment with different F regimens. Experiments will be conducted to separate the effects of initial F exposure during topical F application from the effects of F-retention in the mouth after the initial application. Additional experiments will evaluate the effects of daytime vs. nighttime F treatment. The objectives of the study are: a) to compare F concentrations in whole saliva with ductal saliva, plaque, enamel, oral soft tissue and interproximal spaces after the use of different home-use F regimens; b) to compare a standardized subject panel with an edentulous panel, a periodontally involved panel, and an hyposalivatory panel, in regard to F-retention. (c) to evaluate the relationship between F-retention, and enamel remineralization and F-uptake over periods of 1, 7 and 14 days; (d) to compare remineralizing effect of the initial contact of topical F with teeth with the effect of F retained in the oral environment after F treatment. The proposed research is expected to provide a deeper understanding of fluoride retention, its role in the caries process, and how this can be exploited to improve caries preventive methods.